The internal resistance of battery and dc generator - help, I'm stuck.

Discussion in 'Homework Help' started by Christine Grech, May 31, 2015.

  1. Christine Grech

    Thread Starter New Member

    May 31, 2015
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    I need to solve this, but I need help...

    'A battery having an emf of 105V and an internal resistance of 1 Ohm is connected in parallel with a d.c generator of emf 110V and internal resistance of 0.5 Ohm to supply a load having a resistance of 8 Ohms. Calculate: a) the currents in the battery, the generator and the load; b) the potential difference across the load.'

    For question number a), is it right if I use 'V=Emf-Ir' please?
     
  2. LDC3

    Active Member

    Apr 27, 2013
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    A good place to start is to draw a diagram with the 2 voltage sources and the 3 resistances.
     
  3. shteii01

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    Feb 19, 2010
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    ^ what he said.
     
  4. Christine Grech

    Thread Starter New Member

    May 31, 2015
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    I did draw it. Can you please tell me if V = Emf - Ir is the right equation to use for question number a)? Thank you.
     
  5. LDC3

    Active Member

    Apr 27, 2013
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    If both positive terminals of the voltage sources are connected together, than that equation only tells you the voltage across the battery, not the voltage across the load.
     
  6. Christine Grech

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    May 31, 2015
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    Ok so it is wrong, thank you.
     
  7. bertus

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    Apr 5, 2008
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    Hello,

    As asked, post your schematic here, so we can have a look you made a correct one.
    You can do this using the "Upload a File" button below the reply box.

    Bertus
     
  8. shteii01

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    Feb 19, 2010
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    Part a asks you to find 3 things. To find 3 things, you need 3 equations.
     
  9. ericgibbs

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    Jan 29, 2010
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    Hi CG,
    Is this your diagram.?

    EMF is the open circuit voltage, so the V will be EMF - Iamp

    But more maths are required to solve the problem.
    E
     
  10. Lestraveled

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    May 19, 2014
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    Sounds like a job for Kirchoff's laws.
     
  11. shteii01

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    Feb 19, 2010
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    yep
     
  12. Christine Grech

    Thread Starter New Member

    May 31, 2015
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    Oh, ok so I have to use Kirchoff's law. Thank you all. Also, thank you ericgibbs, for your diagram as I had drawn it in a different way, and did not realise what equation to use.
     
  13. shteii01

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    Feb 19, 2010
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    How do you know that their's is right?
     
  14. ericgibbs

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    Who is theirs.???
    Mine or the OP's.

    My drawing was created from the very clear description posted by the OP.
     
  15. shteii01

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    Feb 19, 2010
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    OP did not post any drawing or schematic.
     
  16. ericgibbs

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  17. Christine Grech

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    May 31, 2015
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  18. ericgibbs

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    In the Top menu bar of this page , is an option named Text books, click and find the topic that you need help with.
    E
     
  19. JoeJester

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    Apr 26, 2005
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    I found it easier to use the Norton equivalent of the two sources and then find the equivalent resistance of the internals and the load.
     
  20. Christine Grech

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    May 31, 2015
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    Thank you.
     
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